Before this change, bisync had no mechanism to gracefully cancel a sync early
and exit in a clean state. Additionally, there was no way to recover on the
next run -- any interruption at all would cause bisync to require a --resync,
which made bisync more difficult to use as a scheduled background process.
This change introduces a "Graceful Shutdown" mode and --recover flag to
robustly recover from even un-graceful shutdowns.
If --recover is set, in the event of a sudden interruption or other un-graceful
shutdown, bisync will attempt to automatically recover on the next run, instead
of requiring --resync. Bisync is able to recover robustly by keeping one
"backup" listing at all times, representing the state of both paths after the
last known successful sync. Bisync can then compare the current state with this
snapshot to determine which changes it needs to retry. Changes that were synced
after this snapshot (during the run that was later interrupted) will appear to
bisync as if they are "new or changed on both sides", but in most cases this is
not a problem, as bisync will simply do its usual "equality check" and learn
that no action needs to be taken on these files, since they are already
identical on both sides.
In the rare event that a file is synced successfully during a run that later
aborts, and then that same file changes AGAIN before the next run, bisync will
think it is a sync conflict, and handle it accordingly. (From bisync's
perspective, the file has changed on both sides since the last trusted sync,
and the files on either side are not currently identical.) Therefore, --recover
carries with it a slightly increased chance of having conflicts -- though in
practice this is pretty rare, as the conditions required to cause it are quite
specific. This risk can be reduced by using bisync's "Graceful Shutdown" mode
(triggered by sending SIGINT or Ctrl+C), when you have the choice, instead of
forcing a sudden termination.
--recover and --resilient are similar, but distinct -- the main difference is
that --resilient is about _retrying_, while --recover is about _recovering_.
Most users will probably want both. --resilient allows retrying when bisync has
chosen to abort itself due to safety features such as failing --check-access or
detecting a filter change. --resilient does not cover external interruptions
such as a user shutting down their computer in the middle of a sync -- that is
what --recover is for.
"Graceful Shutdown" mode is activated by sending SIGINT or pressing Ctrl+C
during a run. Once triggered, bisync will use best efforts to exit cleanly
before the timer runs out. If bisync is in the middle of transferring files, it
will attempt to cleanly empty its queue by finishing what it has started but
not taking more. If it cannot do so within 30 seconds, it will cancel the
in-progress transfers at that point and then give itself a maximum of 60
seconds to wrap up, save its state for next time, and exit. With the -vP flags
you will see constant status updates and a final confirmation of whether or not
the graceful shutdown was successful.
At any point during the "Graceful Shutdown" sequence, a second SIGINT or Ctrl+C
will trigger an immediate, un-graceful exit, which will leave things in a
messier state. Usually a robust recovery will still be possible if using
--recover mode, otherwise you will need to do a --resync.
If you plan to use Graceful Shutdown mode, it is recommended to use --resilient
and --recover, and it is important to NOT use --inplace, otherwise you risk
leaving partially-written files on one side, which may be confused for real
files on the next run. Note also that in the event of an abrupt interruption, a
lock file will be left behind to block concurrent runs. You will need to delete
it before you can proceed with the next run (or wait for it to expire on its
own, if using --max-lock.)
Before this change, bisync could only detect changes based on modtime, and
would refuse to run if either path lacked modtime support. This made bisync
unavailable for many of rclone's backends. Additionally, bisync did not account
for the Fs's precision when comparing modtimes, meaning that they could only be
reliably compared within the same side -- not against the opposite side. Size
and checksum (even when available) were ignored completely for deltas.
After this change, bisync now fully supports comparing based on any combination
of size, modtime, and checksum, lifting the prior restriction on backends
without modtime support. The comparison logic considers the backend's
precision, hash types, and other features as appropriate.
The comparison features optionally use a new --compare flag (which takes any
combination of size,modtime,checksum) and even supports some combinations not
otherwise supported in `sync` (like comparing all three at the same time.) By
default (without the --compare flag), bisync inherits the same comparison
options as `sync` (that is: size and modtime by default, unless modified with
flags such as --checksum or --size-only.) If the --compare flag is set, it will
override these defaults.
If --compare includes checksum and both remotes support checksums but have no
hash types in common with each other, checksums will be considered only for
comparisons within the same side (to determine what has changed since the prior
sync), but not for comparisons against the opposite side. If one side supports
checksums and the other does not, checksums will only be considered on the side
that supports them. When comparing with checksum and/or size without modtime,
bisync cannot determine whether a file is newer or older -- only whether it is
changed or unchanged. (If it is changed on both sides, bisync still does the
standard equality-check to avoid declaring a sync conflict unless it absolutely
has to.)
Also included are some new flags to customize the checksum comparison behavior
on backends where hashes are slow or unavailable. --no-slow-hash and
--slow-hash-sync-only allow selectively ignoring checksums on backends such as
local where they are slow. --download-hash allows computing them by downloading
when (and only when) they're otherwise not available. Of course, this option
probably won't be practical with large files, but may be a good option for
syncing small-but-important files with maximum accuracy (for example, a source
code repo on a crypt remote.) An additional advantage over methods like
cryptcheck is that the original file is not required for comparison (for
example, --download-hash can be used to bisync two different crypt remotes with
different passwords.)
Additionally, all of the above are now considered during the final --check-sync
for much-improved accuracy (before this change, it only compared filenames!)
Many other details are explained in the included docs.
Before this change, bisync intentionally ignored Google Docs (albeit in a
buggy way that caused problems during --resync.) After this change, Google Docs
(including Google Sheets, Slides, etc.) are now supported in bisync, subject to
the same options, defaults, and limitations as in `rclone sync`. When bisyncing
drive with non-drive backends, the drive -> non-drive direction is controlled
by `--drive-export-formats` (default `"docx,xlsx,pptx,svg"`) and the non-drive
-> drive direction is controlled by `--drive-import-formats` (default none.)
For example, with the default export/import formats, a Google Sheet on the
drive side will be synced to an `.xlsx` file on the non-drive side. In the
reverse direction, `.xlsx` files with filenames that match an existing Google
Sheet will be synced to that Google Sheet, while `.xlsx` files that do NOT
match an existing Google Sheet will be copied to drive as normal `.xlsx` files
(without conversion to Sheets, although the Google Drive web browser UI may
still give you the option to open it as one.)
If `--drive-import-formats` is set (it's not, by default), then all of the
specified formats will be converted to Google Docs, if there is no existing
Google Doc with a matching name. Caution: such conversion can be quite lossy,
and in most cases it's probably not what you want!
To bisync Google Docs as URL shortcut links (in a manner similar to "Drive for
Desktop"), use: `--drive-export-formats url` (or alternatives.)
Note that these link files cannot be edited on the non-drive side -- you will
get errors if you try to sync an edited link file back to drive. They CAN be
deleted (it will result in deleting the corresponding Google Doc.) If you
create a `.url` file on the non-drive side that does not match an existing
Google Doc, bisyncing it will just result in copying the literal `.url` file
over to drive (no Google Doc will be created.) So, as a general rule of thumb,
think of them as read-only placeholders on the non-drive side, and make all
your changes on the drive side.
Likewise, even with other export-formats, it is best to only move/rename Google
Docs on the drive side. This is because otherwise, bisync will interpret this
as a file deleted and another created, and accordingly, it will delete the
Google Doc and create a new file at the new path. (Whether or not that new file
is a Google Doc depends on `--drive-import-formats`.)
Lastly, take note that all Google Docs on the drive side have a size of `-1`
and no checksum. Therefore, they cannot be reliably synced with the
`--checksum` or `--size-only` flags. (To be exact: they will still get
created/deleted, and bisync's delta engine will notice changes and queue them
for syncing, but the underlying sync function will consider them identical and
skip them.) To work around this, use the default (modtime and size) instead of
`--checksum` or `--size-only`.
To ignore Google Docs entirely, use `--drive-skip-gdocs`.
Nearly all of the Google Docs logic is outsourced to the Drive backend, so
future changes should also be supported by bisync.
Refactored the case / unicode normalization logic to be much more efficient,
and fix the last outstanding issue from #7270. Before this change, we were
doing lots of for loops and re-normalizing strings we had already normalized
earlier. Now, we leave the normalizing entirely to March and avoid
re-transforming later, which seems to make a large difference in terms of
performance.
Before this change, --resync was handled in three steps, and needed to do a lot
of unnecessary work to implement its own --ignore-existing logic, which also
caused problems with unicode normalization, in addition to being pretty slow.
After this change, it is refactored to produce the same result much more
efficiently, by reducing the three steps to two and letting ci.IgnoreExisting
do the work instead of reinventing the wheel.
The behavior and sync order remain unchanged for now -- just faster (but see
the ongoing lively discussions about potential future changes in #5681!)
Before this change, Bisync sometimes normalized NFD to NFC and sometimes
did not, causing errors in some scenarios (particularly for users of macOS).
It was similarly inconsistent in its handling of case-insensitivity.
There were three main places where Bisync should have normalized, but didn't:
1. When building the list of files that need to be transferred during --resync
2. When building the list of deltas during a non-resync
3. When comparing Path1 to Path2 during --check-sync
After this change, 1 and 3 are resolved, and bisync supports
--no-unicode-normalization and --ignore-case-sync in the same way as sync.
2 will be addressed in a future update.
Before this change, bisync needed to build a full listing for Path1, then a
full listing for Path2, then compare them -- and each of those tasks needed to
finish before the next one could start. In addition to being slow and
inefficient, it also caused real problems if a file changed between the time
bisync checked it on Path1 and the time it checked the corresponding file on
Path2.
This change solves these problems by listing both paths concurrently, using
the same March infrastructure that check and sync use to traverse two
directories in lock-step, optimized by Go's robust concurrency support.
Listings should now be much faster, and any given path is now checked
nearly-instantaneously on both sides, minimizing room for error.
Further discussion:
https://forum.rclone.org/t/bisync-bugs-and-feature-requests/37636#:~:text=4.%20Listings%20should%20alternate%20between%20paths%20to%20minimize%20errors
